Improve file type check for AAR (#1987)

* Initial plan

* Update AAR detection to check actual file content instead of extension

Co-authored-by: Goooler <10363352+Goooler@users.noreply.github.com>

* Update JavaPluginsTest.kt

* Reformat

* Check extension as well

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Goooler <10363352+Goooler@users.noreply.github.com>
Co-authored-by: Zongle Wang <wangzongler@gmail.com>

Author: Copilot

src/functionalTest/kotlin/com/github/jengelman/gradle/plugins/shadow/JavaPluginsTest.kt

@@ -853,7 +853,7 @@ class JavaPluginsTest : BasePluginTest() {
 
   @Test
   fun failBuildIfProcessingAar() {
-    val fooAarPath = path("foo.aar")
+    val fooAarPath = buildJar("foo.aar") { insert("AndroidManifest.xml", "<manifest/>") }
 
     projectScript.appendText(
       """

src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/tasks/ShadowJar.kt

@@ -26,6 +26,8 @@ import com.github.jengelman.gradle.plugins.shadow.transformers.ServiceFileTransf
 import java.io.File
 import java.io.IOException
 import java.util.jar.JarFile
+import java.util.zip.ZipException
+import java.util.zip.ZipFile
 import javax.inject.Inject
 import kotlin.reflect.full.hasAnnotation
 import org.apache.tools.zip.Zip64Mode
@@ -451,7 +453,7 @@ public abstract class ShadowJar : Jar() {
         file.isDirectory -> {
           from(file)
         }
-        file.extension.equals("aar", ignoreCase = true) -> {
+        file.extension.equals("aar", ignoreCase = true) && file.isAar() -> {
           val message =
             """
             Shadowing AAR file is not supported.
@@ -666,3 +668,11 @@ public abstract class ShadowJar : Jar() {
     }
   }
 }
+
+private fun File.isAar(): Boolean =
+  try {
+    ZipFile(this).use { zip -> zip.getEntry("AndroidManifest.xml") != null }
+  } catch (_: ZipException) {
+    // File is not a valid ZIP, so it cannot be an AAR.
+    false
+  }